1. Field of the Invention
The present invention relates to a coordinates input apparatus and, more particularly, to a coordinates input apparatus in which a vibration which is input from a vibration pen to a vibration propagating plate is detected by vibration sensors attached to the vibration propagating plate and the coordinates of the vibration input point of the vibration pen are detected.
2. Related Background Art
Hitherto, as an apparatus for inputting hand written characters, figures, or the like to a processing apparatus such as a computer, various kinds of coordinates input apparatuses using an input pen, tablet, or the like have been known. According to such a kind of system, image information consisting of input characters, figures, or the like is output to a display device such as a CRT display or a recording apparatus such as a printer.
In this kind of apparatus, the supersonic vibration which is propagated from the vibration input pen to the tablet is input to the vibration propagating plate and detected by the vibration sensors attached to predetermined portions on the vibration propagating plate which are away from the input point. The coordinates of the input point are determined on the basis of the vibration propagation times to the respective sensors.
According to such a system using the supersonic vibration, the input tablet can be made of a transparent material such as acrylic plate, glass plate, or the like. Therefore, it is possible to construct an information input/output apparatus in which the input tablet is overlaid onto a liquid crystal display device or the like and which can be used with a good operating feeling such that an image is written onto a paper.
In the above coordinates input apparatus, piezoelectric device or the like is used as an electric/mechanical or mechanical/electric converting device constituting a vibrator or vibration sensors.
Such a vibration converting device is fixed to the vibration propagating plate of the tablet or a member such as a horn at the tip of the vibration pen by adhering or pressure contacting or the like. When the vibration converting device is fixed by the adhering method, there are problems such that the vibration propagating characteristic changes due to an adhesive agent, a variation in vibration propagating characteristic occurs in dependence on an amount of deposition of the adhesive agent, and the like.
In the case of fixing the vibration converting divice by the pressure contacting method using a spring or the like, such a problem of the large variation in vibration propagating characteristic does not occur. However, because of the roughness or the like of the edge surface of the device, an air layer is formed between the device edge surface and the surface onto which the device is come into pressure contact. Even if the pressure contacting conditions are properly adjusted, a variation still occurs in the vibration propagating characteristic. In particular, since an electrode is attached to the edge surface of the coverting device, in the case of a structure such that a conductive member made of silver or the like is adhered as shown in FIG. 4, it is difficult to set the shape of the edge surface to be constant. Thus, the variation in vibration porpagating characteristic increases.
Therefore, according to the system in which the vibration detection timing is decided on the basis of the waveform process and the coordinates are calculated, there are problems such that differences occur among the detection coordinates values and a constant coordinates detection accuracy cannot be assured every product.
The change in vibration propagating characteristic occurs in the pressure contacting portion of the vibrator of the vibration pen and in the pressure contacting portions among the vibration propagating plate of the tablet and the vibration sensors. Therefore, even if a variation in vibration propagating characteristic which occurs in each portion is small, a fairly large variation in characteristic eventually occurs.
Further, the vibration propagating plate such as metal plate, glass, plastics, or the like is used as the tablet. The mechanical/electric or electric/mechanical converting device such as a piezo-electric device or the like is used as a vibration sensor which is attached to the tablet or as a supersonic vibrator which is attached to the input pen.
Particularly, the vibrator attached to the input pen propagates the supersonic vibration to the vibration propagating plate of the tablet through the vibration propagating member such as a horn. On the other hand, to give a drive signal to the vibrator, a signal line needs to be connected to the electrode of the device. In this case, hitherto, a lead wire is soldered to the electrode of the device.
However, there is a problem such that the characteristic of the vibrator changes due to a solder which is used to connect the lead wire to the electrode. That is, in order to improve the vibration propagating characteristic, the vibrator is designed and manufactured so as to have a predetermined resonant characteristic. However, when the solder is deposited to a part of the device, the physical vibrating characteristic changes, so that a desired vibration propagating characteristic cannot be obtained.
On the other hand, it is difficult to always accurately and uniformly solder every product at the proper attaching positions or with correct amounts of deposition of the solder, causing a problem such that the characteristics differ every input pen.
On the contrary, a method whereby after the solder was deposited to the vibrators, the characteristics of the devices are adjusted to obtain the uniform characteristics is also considered. However, it is considered that such adjusting works become extremely hard. This manufacturing method is improper in terms of high productivity.